{
 "version": "2026-10-20",
 "license": "Dimension sheets: CC BY 4.0. Standard and published-size files: CC BY 4.0. Xem Studio's own designs (files_license = Xem Studio Design License): free to use and sell things from, not to redistribute as files — https://xemstudio.com/license/. Other publishers' files: their own license, linked beside them.",
 "slug": "crane-strap-brake-mechanism",
 "name": "Crane strap brake: steel strap round a drum, tightened by a lever",
 "kind": "hardware",
 "category": "Mechanisms",
 "group": "Belt and friction drives",
 "year": null,
 "question": "How does a strap (band) brake work?",
 "tags": [
  "mechanism",
  "belt and friction drives",
  "kinematics",
  "507 mechanical movements"
 ],
 "aliases": [
  "band brake",
  "strap brake",
  "crane brake",
  "drum brake band",
  "freno de cinta de grúa",
  "Bandbremse (Kranbremse)"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": false,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/crane-strap-brake-mechanism/",
 "sheet_txt": "https://xemstudio.com/objects/crane-strap-brake-mechanism/sheet.txt",
 "sheet": {
  "basis": "Xem Studio design following Brown No. 242 (1868)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A steel strap wraps most of the way round a drum on the hoist shaft. One end is anchored on the lever's fulcrum, the other on the lever close to it, so pressing the handle pulls the strap tight round the drum. Its grip grows along the wrap: the tension ratio between the ends is e^(μθ), 3.31 for μ = 0.3 over the 228.78° drawn, and the brake torque is (T1 − T2) × R.",
   "Drum Ø60 × 20, strap 20 × 1.5 touching the drum over 228.78° with both legs tangent, pins 24 mm apart 48 mm below the axis, lever handle 142 mm from the fulcrum. Drawn snug, lever level.",
   "Brown's No. 242 (strap brake used on cranes).",
   "Parts (each has its own page): brake-drum-60x20-bore10, brake-strap-20x1-5-drum60-pins24, strap-brake-lever-130-pins24, dowel-pins-metric, linear-shafts-h6.",
   "Brown's movement No. 242 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "drum",
     "Ø60"
    ],
    [
     "wrap",
     "228.78°"
    ],
    [
     "tension ratio (μ 0.3)",
     "3.31"
    ],
    [
     "lever ratio",
     "≈ 6 : 1"
    ]
   ]
  }
 },
 "sheet_text": "Crane strap brake: steel strap round a drum, tightened by a lever — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/crane-strap-brake-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)\nBasis: Xem Studio design following Brown No. 242 (1868)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A steel strap wraps most of the way round a drum on the hoist shaft. One end is anchored on the lever's fulcrum, the other on the lever close to it, so pressing the handle pulls the strap tight round the drum. Its grip grows along the wrap: the tension ratio between the ends is e^(μθ), 3.31 for μ = 0.3 over the 228.78° drawn, and the brake torque is (T1 − T2) × R.\n- Drum Ø60 × 20, strap 20 × 1.5 touching the drum over 228.78° with both legs tangent, pins 24 mm apart 48 mm below the axis, lever handle 142 mm from the fulcrum. Drawn snug, lever level.\n- Brown's No. 242 (strap brake used on cranes).\n- Parts (each has its own page): brake-drum-60x20-bore10, brake-strap-20x1-5-drum60-pins24, strap-brake-lever-130-pins24, dowel-pins-metric, linear-shafts-h6.\n- Brown's movement No. 242 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.\n\nparameter  value\ndrum  Ø60\nwrap  228.78°\ntension ratio (μ 0.3)  3.31\nlever ratio  ≈ 6 : 1\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Henry T. Brown (1868, public domain): Five Hundred and Seven Mechanical Movements — scan on archive.org — web — Publisher's page; dimensions are facts — https://archive.org/details/fivehundredseven00browiala\n- 507movements.com: Brown's movement No. 242: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_242.html\n\nFree files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/crane-strap-brake-mechanism/index.json\nAPI: https://xemstudio.com/api/geometry?object=crane-strap-brake-mechanism\n",
 "sources": [
  {
   "publisher": "Henry T. Brown (1868, public domain)",
   "title": "Five Hundred and Seven Mechanical Movements — scan on archive.org",
   "url": "https://archive.org/details/fivehundredseven00browiala",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "507movements.com",
   "title": "Brown's movement No. 242: figure, his text and an animation",
   "url": "https://507movements.com/mm_242.html",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "brake-drum-60x20-bore10",
  "brake-strap-20x1-5-drum60-pins24",
  "strap-brake-lever-130-pins24",
  "dowel-pins-metric",
  "linear-shafts-h6"
 ],
 "fits": [],
 "dimensions": "exact (nominal, no printing tolerance)",
 "dimension_rule": "All geometry on Xem Studio is exact (nominal, true size) with no printing tolerance. Where a part meets another part, the object lists its mating features (feature, exact size, what it mates with, fit class: press, slide, run, socket, clamp or designed). Apply your process's allowance to those features only; 'designed' gaps are part of the design and stay as drawn.",
 "mating": [],
 "faq": [
  {
   "q": "How does a strap (band) brake work?",
   "a": "A steel strap wraps most of the way round a drum on the hoist shaft. One end is anchored on the lever's fulcrum, the other on the lever close to it, so pressing the handle pulls the strap tight round the drum. Its grip grows along the wrap: the tension ratio between the ends is e^(μθ), 3.31 for μ = 0.3 over the 228.78° drawn, and the brake torque is (T1 − T2) × R."
  }
 ],
 "files_license": {
  "name": "Xem Studio Design License",
  "holder": "Xem Studio",
  "url": "https://xemstudio.com/license/",
  "note": "Xem Studio's own design: free to use, print, modify and sell things made from it; not to be republished or redistributed as files."
 },
 "offers": [
  {
   "file": "crane-strap-brake-mechanism-assembly",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "Xem Studio Design License",
   "step": "https://xemstudio.com/files/hardware/crane-strap-brake-mechanism/crane-strap-brake-mechanism-assembly.step",
   "stl": "https://xemstudio.com/files/hardware/crane-strap-brake-mechanism/crane-strap-brake-mechanism-assembly.stl",
   "note": "Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/crane-strap-brake-mechanism/index.md"
}